1. Field of the Invention
The present invention relates to an improved process for producing an electrophotographic material, more particularly, to a process for producing an electrophotographic material having at least one film-forming resin layer free of pinholes.
2. Description of the Prior Art
Electrophotographic light-sensitive materials comprising a support, such as paper, having provided thereon a zinc oxide/resin dispersion type photoconductive insulating layer or an organic photoconductive layer mainly comprising polyvinyl carbazole, are widely used in the copying field.
However, when a so-called liquid developing method is used to develop such materials, the following problems are encountered. In many cases, the back surface or surface free of a light-sensitive layer of such a material is also provided with a resin layer, and fine pinholes unavoidably lie scattered throughout the layer. A liquid developer is liable to penetrate through these pinholes into the interior of the paper support, resulting in the formation of undesirable spot-like stains on the back side of a finished print, as well as increasing the drying load and consumption of developer.
When the back surface is not coated in any manner to permit the free penetration (absorption) of liquid over the whole surface and the processing solution is squeezed at the end of processing followed by forced drying, stains are uniformly formed over the whole surface since the liquid is freely volatized from the paper, and hence there are comparatively less problems regarding the drying load and the wastage rate of the liquid.
However, where a film capable of preventing a liquid from penetrating into a light-sensitive material to a considerable degree is provided, the liquid is difficult to volatize once it penetrates into the light-sensitive material, which results in spot-like, non-dryable regions which remain over a long period of time.
As one solution to these problems, methods of reducing the number of pinholes have been suggested, e.g., making a film thick to such an extent that almost no liquid penetration is observed during processing with a liquid, and conducting processing in two steps wherein the back surface is first processed with a carrier liquid for a developing agent to penetrate a colorless, toner-free liquid into the support.
The former method, however, is economically disadvantageous since the film must be thick. For example, in order to try to attain the above-described object, resins such as polyvinyl alcohol must be applied in an amount of about 5 g/m.sup.2 to the back side of the light-sensitive material. This seriously affects the mechanical properties of the resulting paper and imposes additional restrictions on the processing of the opposite surface from the point of curling balance or the like, as well as lowering the flexibility and feel which is characteristic of paper. Thus, the application of a resin film in such an amount is not preferred. In addition, even at such a coating amount, resins capable of constituting a closed layer are restricted as to kind, which seriously narrows the degree of freedom in setting up production conditions.
The latter method involves the defects that it requires complicated apparatus since the processing is conducted in two steps and that non-dryable spots remain as in the first method, though no stains are left after drying since the penetrating liquid contains no toner. These non-dryable spots cause problems in the case of, e.g., obtaining color images and the like by a superposition development.
Further, when a photoconductive-pigment layer coating dispersion is coated on a resin coated porous support, the dispersion penetrates into the resin layer through pinholes in the resin layer, and after drying many hillocks are observed on the coated surface. The hillocks are produced by deposition of photoconductive particles at the pinholes, the particles piling up after the resin contained in the dispersion penetrates into the support. The image quality obtained using such an electrophotographic material is very poor due to the rough surface, i.e., optical density is low and fogging is significant.